Thranduil's halls is the name given to the cave system in northern Mirkwood, which the Elves of Mirkwood lived during most of the Third Age and Fourth Age. They may have been built by Thranduil, possibly when darkness entered the wood; or it may be that they were built in Oropher's time or even before. It is reminiscent of Menegroth, the capital of Doriath where both Oropher and Thranduil originally lived.